And I'm Audie Cornish. President Obama now says 8 million Americans have signed up for health insurance coverage on the new government exchanges. That's a half million more than previously announced. The president made the announcement during an impromptu news conference at the White House this afternoon where he also discussed ongoing tensions in Ukraine.

NPR's Scott Horsley joins us now to. And Scott, a lot of people were actually surprised at the beginning of this month when the White House said that they're reached their original target of signing up 7 million people on the government exchanges. Now it seems those numbers are even better.

SCOTT HORSLEY, BYLINE: Yeah, 7 million was a surprise. 8 million is an even bigger surprise. Of course, the White House had said that people who were in line, who'd started the process when the March 31 deadline hit, would be allowed to complete. And what we're learning is there were a lot of people in line at the end of that sign-up window. We're also learning a little bit about the demographics of who was in line and that the people who waited until the last minute tended to skew younger. That's what we expected. But it's also a positive because younger people tend to be a little bit less costly to insure.

The president said today that of those who signed up on the federal exchange - not the state exchanges, but the federal exchange - 35 percent were under the age of 35.

PRESIDENT BARACK OBAMA: This thing is working. I've said before, this law won't solve all the problems in our healthcare system. We know we've got more work to do. But we now know for a fact that repealing the Affordable Care Act would increase the deficit, raise premiums for millions of Americans and take insurance away from millions more, which is why, as I've said before, I find it strange that the Republican position on this law is still stuck in the same place that it has always been.

HORSLEY: There was also more evidence from a Gallup survey this week that the number of people who are uninsured is going down, and it's going down fastest in those states that most fully embrace the healthcare law in particular by expanding Medicaid.

CORNISH: Meanwhile, the president met with insurance executives and state regulators today. They're looking ahead to what the premiums will be next year. What have we learned about that?

HORSLEY: Well, it's still a guessing game. I mean, knowing the ages of the people signing up is helpful, but it's really going to be months before we what it's going to cost to insure this population and what the premiums will need to be going forward. This week we did see a forecast from the experts at the congressional budget office that they expect premiums to be lower previously thought. Obama says that has positive ripple effects throughout the economy. He also says the healthcare law is helping to keep a lid on healthcare inflation generally.

OBAMA: Those savings add up to more money that families can spend at businesses, more money that businesses can spend hiring new workers and the CBO now says that the Affordable Care Act will be cheaper than recently projected.

HORSLEY: Now, there's a mixed blessing here because one of the reasons the premiums are expected to be lower, the CBO says, is because a lot of insurance companies are using narrow networks, fewer choices for consumers. So there is a possible tension there between what consumers want, lots of choice, and what they want to pay for.

CORNISH: Finally Scott, President Obama was asked about the tentative agreement to ease tensions in Ukraine. How confident is the administration about this deal?

HORSLEY: This is the tentative agreement that was reached after seven hours of talks in Geneva today between American, European, and Russian negotiators. It was an effort to deescalate the tensions in Ukraine by disarming militias for example, having people move out of occupied buildings. Secretary of State John Kerry called it a good day's work, but he cautioned words on paper will have little meaning unless matched with action. And at the White House, President Obama echoed that caution.

OBAMA: I don't think we can be sure of anything at this point. I think there is the possibility, the prospect, that diplomacy may deescalate the situation and we may be able to move towards what has always been our goal, which is let the Ukrainians make their own decisions about their own lives.

HORSLEY: Secretary Kerry warned that if there is no improvement on the ground in Ukraine, the U.S. will have no choice but to ratchet up its economic sanctions.